Some fats and oils contain high free fatty acid content, including but not limited to corn oil and waste fats and oils. As is generally known in the art, fats and oils containing a high percentage of free fatty acids are undesirable. For example, free fatty acids decrease the oxidative stability of oil. Previous methods include the refining of crude oils, which generally result in oil of low free fatty acid content. The crude oils, which have low free fatty acid content, are purified by converting the fatty acids to soaps using caustic or alkali and then separating the free fatty acid soaps, commonly referred to as soapstock, from the oil. The soapstock is then treated as a waste product or used for animal feed and soap manufacturing. These methods fail to capitalize on the potential of free fatty acids as a valuable product within the fats and oils industry. For example, recovered free fatty acids may be used in feed fat supplements and to manufacture industrial products. Moreover, previous methods lead to the formation of an emulsion that entraps neutral oil, thus resulting in a high neutral oil loss. The neutral oil loss is exacerbated in the case of waste fats and oils due to the presence of high free fatty acid content. This is problematic because neutral oil is a valuable product. Accordingly, an ideal method will minimize neutral oil loss.
As provided above, fats and oils with high free fatty acids may include corn oil and waste fats and oils. For example, corn oil, including but not limited to corn oil that is produced as a byproduct of an ethanol production plant, may include at least 4% free fatty acids by weight. Other fats and oils with high free fatty acid content include high acid grease from pork plants, high acid tallow from beef plants, waste fryer grease, and sorghum wheat oil, such as from an ethanol plant utilizing sorghum. Moreover, a byproduct of biodiesel production may include unreacted fats and oils with high free fatty acid content. Generally, all of these fats and oils are inedible, industrial and fall into secondary or tertiary grade fats and oils. They may have a free fatty acid content of up to 90%. Processing these fats and oils to recover the free fatty acids results in at least two valuable products: neutral oil and free fatty acids. Additionally, other impurities that are removed in the method may be valuable products.
Previous attempts have been made to remove free fatty acids from oil, particularly crude oil having low free fatty acid content. These methods have drawbacks. In particular, these methods are unsuccessful when removing free fatty acids from starting material having high free fatty acid content. For example, the methods are ineffective when recovering free fatty acids from corn oil produced at an ethanol production facility and waste fats and oils. Oftentimes, these methods include adding alkali to the oil to create free fatty acid soaps. However, the addition of alkali to fats and oils having high free fatty acid content results in an emulsion. The emulsion includes fatty acid soaps and neutral oil and must be further processed to remove these valuable substances. Alternatively, if the emulsion is not processed, the recovery of both fatty acids and neutral oil will be reduced, resulting in a loss of valuable products. Moreover, because previous attempts to remove free fatty acids from fats and oils are directed to refining crude oil, the methods fail to capture free fatty acids as a valuable product.
In one example, United Kingdom Patent Specification No. 427,680 discloses a process for refining vegetable and animal oils and fats. The invention described therein relates to the separation of fatty acid soaps formed by free fatty acids and caustic. The disclosed process addresses the problem of an emulsion by treatment with an alcoholic solution of salts sufficiently concentrated to prevent most oil from going into solution. Effective salts include alkali metal salts such as sodium sulfate, chloride, nitrate, formate, and acetate. The reference argues that the salts prevent neutral oil from dissolving in the alcoholic solution. A similar process is disclosed in United Kingdom Patent Specification No. 1,391,906, which discloses a process for the removal of fatty acids from glyceride oils. The process includes mixing the oil with an aqueous alkaline solution including polyhydric alcohol and sulfonate salt.
In another process, United Kingdom Patent Specification No. 430,381 is directed to the recovery of solvents employed during the refining of oils and fats. The reference discloses the process of neutralizing the oil to produce soapstock and drying the fatty acid soaps in a vacuum prior to adding alcohol to the fatty acid soaps. The addition of the alcohol to the dried soapstock forms three layers: neutral oil, soap, and a layer of emulsion. The emulsion layer must then be processed to remove soaps. This process is inefficient in that it requires the steps of drying the fatty acid soaps and processing the emulsion.
Another process, disclosed in United Kingdom Patent Specification No. 596,871 is directed to the refining of vegetable glyceride oils and fats, particularly cottonseed oil. Crude oil having low free fatty acid content is neutralized in the presence of low concentrations of alcohol. The method disclosed therein is particularly applicable to oils having a high content of non-fatty substances, considerable coloring matter, and free fatty acid content around 1-2%. Accordingly, the process is not well-suited for fats and oils having high free fatty acid content and/or low amounts of non-fatty substances and coloring matter. Specifically, the process disclosed therein results in greater neutral oil loss as free fatty acid content increases.
Another reference, U.S. Pat. No. 6,399,802 provides a method for soapstock acidulation. The method includes adding both a monohydric alcohol to soapstock to lower its viscosity and a strong acid which hydrolyzes the fatty acid soaps. The acidulated fatty acids may then be converted to esters utilizing the alcohol already present in the solution, as well as catalysts already present in the solution. Effective alcohols include isopropanol, n-propanol, isoamyl alcohol, and fusel oil.
None of the above methods provides an efficient means for recovering the free fatty acids found in fats and oils having high free fatty acid content. In addition, the above-described methods fail to result in low amounts of neutral oil loss, particularly as free fatty acid content is increased. Moreover, none of the above methods may be easily integrated into an ethanol production facility or capitalize on the products and byproducts associated with same.
Crude vegetable oils that are food grade typically have free fatty acid content of about 1% in addition to other non-oil impurities. These vegetable oils when refined through traditional alkali refining will result in process loss or neutral oil loss due to physical and chemical binding of oil with the co-products that are generated in the process. Although the neutral oil loss varies with different processes, there are some generally accepted empirical equations that are used by the producers to help estimate the neutral oil loss. American Oil Chemists' Society (AOCS) official methods Ca 9f-57 and Ca-9a-52 form the basis for calculating the neutral oil loss due to processing and inevitable loss due to the presence of free fatty acids, phosphatides and other impurities. L. Strecker et al. developed an equation specific to the process loss during the alkali refining of crude corn oil. According to this given formula, neutral oil loss for alkali refining of crude corn oil with 12% free fatty acid content is about 11% in addition to the inevitable loss due to removal of free fatty acids, impurities etc. Corn oil having 4% free fatty acid content may have neutral oil loss around 4.5% in addition to the inevitable loss due to removal of free fatty acids, impurities etc. Previous methods provide the principle that as free fatty acid content increases, so does neutral oil loss, such as the example immediately above.
Accordingly, there exists a need in the art for a method to recover free fatty acids and other impurities from high free fatty acid fats and oils. The method should have as little neutral oil loss as possible and should further recover as many free fatty acids from the neutral oil as possible in order to maximize the value of both products. Further, the method should remove other impurities from the starting materials, including but not limited to carotenoids, phytosterols, tocopherols, phospholipids and waxes. Such a method should be easily integrated into an ethanol production facility by taking advantage of products and byproducts associated with same.